Simultaneous detection and quantification of explosives by a modified hollow cathode discharge ion source.

Detection of explosives at trace levels is crucial for security purposes because of increasing worldwide terrorist threats at public places. Previously, a hollow cathode discharge (HCD) ion source has been fabricated for detection of explosives. Recently, the HCD ion source has been modified for a dual pressures operating system and coupled to a linear ion trap MS to analyze explosives simultaneously. Here, trinitrotoluene (TNT), nitroglycerin (NG), pentaerythritol tetranitrate (PETN) and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) were taken as model explosive compounds and the mass spectra were recorded in the negative mode ionization. At the higher ion source pressure (~28.0–30.0 Torr), NG, PETN and RDX gave adduct ions with the NO 3 − ion while TNT showed the [TNT + NO 3 –HNO 2 ]- (m/z 242) simultaneously. However, NG and PETN did not give any ion signals at the lower ion source pressure (~0.8–1.0 Torr) while TNT exhibited its molecular ion, [TNT]-• (m/z 227), as a major ion through electron attachment and RDX showed fragment ions that followed electron capture dissociation concurrently. The modified HCD ion source exhibited better sensitivity in simultaneous detection and quantification of the explosives. The NO 3 − and NO 2 − as reagent ions in the air HCD plasma form stable adduct ions with the NG, PETN and RDX even with TNT at the higher temperature (140–200 °C). The formation of the NO 3 −, NO 2 − in the HCD plasma also causes the formation of [TNT-H]- (m/z 226) at the higher ion source pressure. The inner metallic surface of the hollow tube assists the Birch reduction type reaction that results in the formation of hydride ion of the TNT, [TNT + H]- (m/z 228). No significant difference in the spectral pattern for simultaneous and individual measurements for the explosives was observed at the higher ion source pressure. Therefore, it may conclude that the present modified HCD ion source can be used for simultaneous detection and quantification of the explosive compounds at trace and/or ultra-trace levels using air as a carrier gas. Simultaneous detection and quantification of explosives by a modified hollow cathode discharge ion source. [Display omitted] • Fabrication of dual pressures hollow cathode discharge ion source. • Simultaneous detection and quantification of explosive compounds. • Adduct ions of NG, TNT, PETN and RDX with NO 3 − at high ion source pressure. • Electron attachment reaction predominates at low ion source pressure. • Birch reduction type reaction causes formation of hydride ion of TNT, [TNT + H]-. [ABSTRACT FROM AUTHOR]